1. Field of the Invention
This invention relates to a method for the preparation of preforms and hollow articles in single-row and multi-row preform and blow molds, respectively, and to an apparatus therefor. The invention represents an improvement in applicant""s prior U.S. Pat. No. 6,217,819 entitled Universal Single Row and Multi Row Insert Stretch Blow Molding Method and Apparatus Therefor. More particularly, the present invention relates to a method and apparatus, wherein during a preform mold opening stroke an entering tray unit collects and removes molten preforms from the molding area. This end is attained by means of a robotic gripper assembly which lifts the preforms either out of the tray unit or from a preform reheat unit, transfers the preforms through different processing phases, adding internal and external components during the transformation into hollow articles, and returns to a waiting position outside the preform molding and tray unit or preform reheat unit.
2. Brief Description of the Prior Art
Heretofore, in conventional prior art molding machines, known as the one-step method, preforms, also called parisons, are injected into a preform mold and transferred by their neck splits which are mounted beneath a horizontal transfer plate in an intermittent rotary motion into a temperature control station, also called conditioning station, an orientation blow molding or stretch blow molding station and a molded product removing or ejection station producing hollow articles in single and double row molds, respectively., as described in U.S. Pat. Nos. 4,946,367, 4,731,011 both to Nissei ASB and Pat. No. 4,457,689 to Aoki respectively. The advantage of this method is that the preforms being held in an upright position can be precisely heat profiled internally with entering touch or conditioning rods. The drawback of this method is that the molten preforms are required to reside in the conditioning station as long it takes to inject and cool the preforms in the preceeding injection station. Heat pots emanating radiant heat are needed to maintain the proper stretch blow temperature, which adversely effects the programmed temperature profiling by the touch or conditioning rods. A technique for overcoming such limitations is described in U.S. Pat. No. 4,941,816 to Aoki U.S. Pat. Nos. 5,062,787 and 5,364,585 both to Aoki Technical Laboratory and U.S. Pat. No. 5,403,177 to Jomar wherein the injected preforms are directly heat conditioned in the preform mold and then immediately transferred into the stretch blow mold. The drawback of this method is that the preform molds are tailored to a specific hollow article geometry. This reduces the number of different hollow article shapes that can be stretch blown from the same preform shape. Unfortunately, such machines also evidence certain limitations, namely in the difficulty of mold interchangeability due to different swing radii and stack heights, the lack of built in automatic oriented discharge and costly neck splits and neck split holders which are required for each station. The vertical clamping forces applied to the neck splits in the preform molds versus the horizontal clamping forces in the blow molds being mounted onto a common rotary plate causes premature wear and tear to the aligning neck split seats. The rotary plates and the machine beds are required to be laid out for the higher clamping forces in the injection station. As a result, the added inertia of the heavy construction and large swing radii of the transfer plates lengthens the dead time of mold open index and mold close, thereby increasing the overall cycle times. Efforts to reduce dry cycle times have been made, as for example, by replacing the rotary tables through closed circuit conveying devices as described in U.S. Pat. No. 4,895,509 To Giacobbe-Magic and U.S. Pat. No. 5,213,822 to Nissei ASB. However, once again, costly support jaws or neck mold sets mounted on slide guides, are required for each station linked together to transfer the preforms and containers through the forming phases in a rectilinear motion in equal distances and equal time intervals. In the rotary-type and chain-link-type method, all phases of preform molding, conditioning, stretch blowing, and discharging are also interdependent due to a common transfer movement. The larger the number and size of transfer components, especially expensive neck splits, for each processing station leads to longer mold changeover times and higher tooling costs. The more machine component weight needs to be transferred, so resulting in slower dry cycles, and thus longer overall cycles.
The industry has recognized these limitations and has also recognized that containers can be conditioned, stretch blown, and discharged in a fraction of the time that it takes to mold the preforms. This discovery has led to a method and apparatus for injection stretch blow molding as described in U.S. Pat. No. 5,468,443 to Nissei ASB wherein a larger number of injection molding stations produce preforms to be conveyed to a lesser number of stretch blow molding stations. The drawback of this method and apparatus is that it requires neck split moving means for supporting and conveying costly neck splits adapted to hold-neck portions of each preform used to mold the hollow articles through all preform molding, conditioning, blow molding, and ejection stations.
Refinements of the aforementioned patent, U.S. Pat. No. 5,468,443 to Nissei ASB are described in U.S. Pat. No. 4,793,960 to Husky, U.S. Pat. Nos. 5,753,279, 5,744,176 and 6,247,916 all to Nissei ASB as well as brochures of Gerosa""s Satellite GE system, SIG""s Ecomax injection stretch blow molding machine and HUSKY""s Index SB system are also known as one and a half step methods wherein molded preforms are first inverted to be released onto carrier members of a circular transfer conveying system. The inverted preforms are then indexed through a reheating section to assure that the first fraction of molded preforms enters the blow mold station with the same temperature profile as the following fractions of simultaneously molded preforms. Once the preforms are stretch blown into final hollow articles, they are inverted again to release them in an upright position. The limitations of these disclosures resides in the fact that the molten preforms are being inverted to be put onto a multitude of neck-size-dependent carrier members. During the inverting process the outside walls of the preforms touch water cooled transfer tubes in an uncontrolled manner, which tends to alter their thermal profile, so leading to uneven wall distributions in the finished hollow articles. The carrier members create a heatsink below the neck areas and, therefore, the reverted preforms need to be excessively heated in the shoulder area, which with long preforms may lead to bending during the intermittent transfer movements. The residence time of each fraction of preforms before entering the reheat oven banks is longer than each following fraction while the residence time in the reheat oven banks is the same for each preform fraction which enters the blow molds consecutively. The bottom up stretch blow molding method reverses the temperature profile of the preforms in the longitudinal direction. The bottom area of the preforms is hotter due to the chimney effect, which leads to preform-sagging and thinner bottoms and heavier shoulders in the hollow articles. Energy consuming cooling fans are installed to overcome this drawback. Preferential heating zones radiate onto the already hot preform outside walls for the production of oval hollow articles. This heat treatment of vertical section of the body of the preform is practiced successfully in so called two-step or reheat stretch blow molding processes because the preforms enter the heating sections at room temperature closely spaced and allow long oven residence times, as disclosed in U.S. Pat. No. 5,681,521 to Sidel and U.S. Pat. No. 6,287,507 to Corpoplast. A second inverting device is needed to release the finished hollow articles in an upright position. The number of injection cavities vs. blow cavities being mechanically coupled remains at a fixed ratio which limits the processing flexibility for instance for lighter-wall vs. heavier-wall containers. A further stretch blow molding concept is described in U.S. Pat. Nos. 4,372,910 and 4,470,796 both to Van Dorn in which molded preforms are picked up by two-row multiple gripper transfer devices, then inserted one row at a time into neck-size dependent collars of the respective closed circuit transportation system to be subsequently indexed to the conditioning, stretch blow and ejection stations. The drawback of this system is that the preforms need to be inserted into a large number of neck-size dependent collars of a transportation system consisting of a common closed loop belt drive which does not allow any timing flexibility between the simultaneous conditioning and stretch blow phases and precludes physical internal heat profiling with touch rods to obtain maximum processing flexibility. As described in European Patent. No. EP 0,768,166B1 to Sipa the thermal conditioning system is required to be twice as long as the stretch blow system to ascertain uniform temperature profiles for the first and second row preforms being introduced. U.S. Pat. No. 4,197,073 to Husky teaches a method, wherein alternate sets of parisons are released into laterally diverging tracks before arriving at the blow-molding unit. Despite the reduction in the number of blow mold cavities, in the end, the number of blowing means is equal to the number of preform mold means. U.S. Pat. No. 4,209,290 to Husky discloses a method wherein blow molding cells are interposed between open injection mold halves and injection cores with their preforms descending into the blow molding cells to form finished bottles. The limitation of this method is that the preform-molding cycle is interrupted during the time it takes to blow-mold the bottles. U.S. Pat. No. 4,310,282 to Emhart-Spurr uses a neck ring carrier to remove the parisons as a group to substitute this transfer with an assembly for the removal by the neck ring carriers which form a portion of the molded parison and a lateral transfer mechanism for positioning the parisons for delivery to the shuttle for final delivery to the blow station. U.S. Pat. No. 4,370,121 to Valyi discloses a multiplicity of tempering molds in spaced relationship to each other for retaining and tempering parisons prior to orientation and blowing. A well suited process for high output production of oriented hollow articles called the two-step method is disclosed in U.S. Pat. No. 6,152,723 to Krones, U.S. Pat. No. 5,863,571 to Sidel and U.S. Pat. No. 4,479,772 to Corpoplast whereby preforms are injection molded, cooled and stored in one location and then transported to a second location where they are unscrambled to be introduced into a reheat stretch blow molding machine. However at equivalent output rates the invention of a single and multi-row one and a half step stretch blow molding method and apparatus based on injection molding technology incorporating quick mold change means (not shown) presents numerous advantages over the two-step method in energy savings, mold change over times, transportation and double handling costs of preforms, less overall floor space requirements and less manpower. In integrated aseptic injection/stretch blow and filling lines the principal advantage over the two-step method is the elimination of chemical sterilants because both the molten preforms and hollow articles are kept sterile when they enter the aseptic filling system. This yields immediate savings in raw material costs and eliminates costly sterilizing/rinsing systems from the line. It prevents the taste of the hollow article contents being altered by residues of sterilants.
U.S. Pat. No. 5,731,014 to Tradesco, U.S. Pat. No. 4,718,845 to Sheffield, and U.S. Pat. No. 4,706,924 to de Larosiere disclose a solution for gaining maximum utilization of molding machines by simply switching mold cavities instead of complete molds in both stack molds and single-face mold versions clamped between a fixed and movable machine platen. This solution works well in conventional injection molding machines. However, in stretch blow molding machines, secondary components such as conditioning rods, blow cores, stretch rods, and bottom plugs, etc. need to be introduced at a predetermined center distance row. European Patent No. EP 0,768,165-A2 to Sipa teaches a method wherein mutually coupled mold plates, connected to a power transmission means, actuate through motion transferring means a double pair of mold halves. U.S. Pat. No. 4,941,816 to Aoki describes a double row clamp molding machine, wherein each blow mold row is closed by lateral pneumatic moving means. Subsequently, pancake cylinders rise between the two rows and expand to apply the necessary clamp pressure against oppositely located clamping means. Both methods are limited to a fixed number of two rows of blow molds at a fixed machine-dependent center row distance. U.S. Pat. No. 6,089,852 to Tradesco discloses a centering arrangement for controlling relative movement between a series of mold support plates in a multi-level stack mold having first and last mold support plates attachable respectively to a fixed and a moveable platen of an injection molding machine and at least two intermediate mold support plates interspersed sequentially therebetween.
U.S. Pat. No. 5,653,934 to Electra Form-Brun discloses a method for removing molded articles from a molding machine whereby article engaging elements comprising a plurality of pairs of elongated bars are placed into channels of the mold body as integral parts of the mold cavities to pick up molded preforms as soon as the mold opens, thereby eliminating the entering stroke for the removal grippers. The drawback of this method is that the available mold width is reduced by the channel spacings needed for the gripper means to enter during the molding phase. U.S. Pat. No. 6,129,883 to Husky discloses a vertical clamp index machine wherein molten preforms are ejected onto a conveyor into receiving means comprising cooled carriers. U.S. Pat. No. 5,273,152 to Electra Form and U.S. Pat. No. 3,753,589 to Holstein and Kappert disclose apparatuses and grippers for altering the center spacing of the article in two directions simultaneously from the first center spacing of the downstream workstation to the second center spacing of the upstream workstation through plate means having a plurality of angled grooves, and a plurality of support members mounted slidably on the plate means. U.S. Pat. No. 4,323,341 to Valyi discloses means for varying the center spacing of the parisons to optimize the parison temperature for orientation and blowing by changing the center spacing of the parison mold and pick up of the parisons with a second set of cores having a center spacing of the blow molds.
U.S. Pat. Nos. 5,362,437 and 5,169,654 both to Nissei ASB disclose a method and apparatus whereby two rows of preforms are conveyed to a blow molding stage by changing the row pitch between the supporting plates when the blowing molds are opened and when the blowing molds are closed for the purpose of reducing the blow molding system in size and occupying area.
U.S. Pat. No. 5,683,729 to Sidel, U.S. Pat. No. 5,110,282 to Nissei ASB, U.S. Pat. No. 4,824,359 to Hoover Universal, and 4,403,907 to Emerson Electric disclose cam-driven rotary pick and place assemblies, which simultaneously carry preforms and hollow articles through the blow molding and release phases. The limitation of such carrying means is that their rotary motion is interdependent, requires space modifying devices and, therefore, does not allow any timing and stroke distance flexibility between the various processing phases. A method for adding external components such as labels, handles, or valves to the preforms or hollow articles is described in U.S. Pat. Nos. 4,479,771 and 4,721,451 both to Plastipak, wherein components, such as labels, are picked up from dispensing heads by the label carrier shuttle and are moved rectilinearly into an open mold wherein they are released onto the mold cavity walls and returned in the same manner to the dispensing head position. The drawback of this method is that the normal blow molding cycle of rotary machines is interrupted to allow the time to introduce the labels into the open mold cavities. Typically, finished containers have to be evacuated first and new preforms need to be delayed from entering the open mold cavities. U.S. Pat. No. 4,983,348 to Wheaton partially overcomes this limitation by opening the upper mold half earlier and inserting labels into the open mold half while holding the previously blown and labeled work pieces or hollow articles in the lower mold half for the duration of the label transfer phase without increasing the overall machine cycle time. The drawback of this method is that only one mold half can receive labels and the distance between the work piece and movable blow mold halves needs to be sufficient to allow the dispensing mechanism to operate in between.
To add secondary components to preforms or hollow articles, U.S. Pat. No. 5,678,771 to Graham Packaging teaches a method wherein an insert is attached on the surface above the threads of a neck finish to maintain stability during and after hot-fill processing. The drawback of this method is that the non-oriented, amorphous neck finish portion beneath the attached reinforced insert can shrink and deform during the hot-fill phase. U.S. Pat. No. 4,988,472 to Nissei ASB teaches a method that prevents the aforementioned-mentioned drawback. However, the insert is placed into a neckring portion of an open mold first and then over-molded with molten material, an operation that lengthens the overall cycle.
U.S. Pat. No. 4,847,129 to Continental PET teaches a method of molding a multi-layer neck-finish structure whereby the center layer consists of a high temperature polymer.
U.S. Pat. No. 5,651,933 to Plastipak and U.S. Pat. No. 3,939,239 to Valyi teach a method wherein thermoformed sleeves are put on injection cores and are over molded to obtain a multi-layer preform. The inner over molded layer needs to be stiff enough to withstand the following injection pressures when injecting the outer layer. Thus, this method requires more costly inner barrier material and is more difficult to bond with the over molded material.
U.S. Pat. No. 5,516,274 to Electra Form describes a movable blow mold clamp assembly permitting improved access for servicing.
1. Purposes of the Invention
It is an object of the present invention to mold preforms in single-row or multi-row preform mold cavities in variable-row spacings to give the molder maximum flexibility in meeting small and large production output requirements. Preform molds can be mounted perpendicular or in line relative to one or several plasticizers.
It is a further object of the invention to enter a tray unit with at least one row of tray plates in between the opening preform mold to collect ejected preforms from above mold halves into their corresponding openings and immediately retract away from the preform molding area.
It is a further object of the invention to hold ejected preforms from above mold halves in corresponding openings of the non heat conducting tray plates with their respective transfer rings.
It is a further object of the invention to hold ejected preforms without transfer rings from above mold halves with their bottom gate sections in non heat conducting catch baskets mounted beneath the tray plate openings
It is a further object of the invention to enter a tray unit with a corresponding number of tray rows than preform mold rows in between the opening preform mold to collect ejected preforms from above mold halves into their corresponding openings and immediately retract away from the preform molding area.
It is a further object of the invention to enter a tray unit with a corresponding number of tray rows than preform mold rows in between the opening preform mold to collect ejected preforms from above mold halves into their corresponding openings and immediately retract away from the preform molding area into the conditioning unit.
It is a further object of the invention to retract the multitude of tray rows away from the molding area in a telescoping manner to align the multitude of tray plate rows with the center row distances of the downstream units.
It is a further object of the invention to transfer the preforms from the tray unit to the downstream units in an upright position.
It is a further object of the invention to utilize a robot with a universal gripper assembly which picks up molded preforms from the retracted tray unit and transfers the same across a conditioning unit into a stretch blow unit to be converted into hollow articles, and then transfers them onto an oriented discharge unit at variable time and stroke intervals before returning to a waiting position at the preform molding unit and the tray unit.
It is a further object of the invention to freely move the robot with the universal gripper assemblies in horizontal and vertical directions to position the preforms into the different processing units to condition, stretch blow and discharge the same.
It is a further object of the invention to lay out the grippers at a multitude of center distances to enable the transfer of preforms and hollow articles with different size neck finishes and at various mold cavity center distances.
It is a further object of the invention for a universal gripper assembly to pick up the molten preforms from the tray unit at the center distance spacings of the preform mold and to telescope the molten preforms into center distance spacings corresponding to the center distance spacings of the blow mold cavity center distances
It is a further object of the invention to utilize a robot with a universal gripper assembly which picks up fractions of molded preforms consecutively from the retracted tray unit and transfers the same across a conditioning unit and into a stretch blow unit to be converted into hollow articles, and then transfers them onto an oriented discharge unit at variable time and stroke intervals before returning to a waiting position at the preform molding and tray unit.
It is a further object of the invention to condition each fraction of preforms consecutively, internally by rows of touch rods, externally by rows of heat pots. It is a further object of the invention whereby a primary robot with a universal gripper assembly picks up a fraction of conditioned performs, transfers the same into at least one row of a stretch blow unit and returns to the conditioning unit to pick up a subsequent fraction of conditioned performs from the tray unit and whereby a secondary robot with a universal gripper assembly picks up hollow articles from at least one row of the stretch blow unit and transfers them onto an oriented discharge unit.
It is a further object of the invention whereby a robot with a universal gripper assembly picks up fractions of conditioned molten preforms from a tray unit transfers them into a stretch blow molding unit and discharge unit which returns to the tray unit to pick up a subsequent fraction of conditioned molten preform to be transferred into the downstream units and eventually returns to a waiting position at the preform molding and tray unit.
It is a further object of the invention whereby a multitude of robots with universal gripper assemblies pick up fractions of conditioned molten preforms from a common tray unit, transfer them into a multitude of stretch blow molding and discharge units and return to their respective waiting positions at the preform molding and tray unit.
It is a further object of the invention to maximize the production capabilities through stack blow molds, wherein the blow mold opening and closing strokes are accelerated by the clamp moving means together with a multitude of helical spindles with helical nuts mounted onto the diverging and converging blow mold clamp platens and pivoting spacing platens aligning the center row distances of the corresponding stretch rod, blow core, and bottom plug assemblies. The number of spacing-platen rows can be increased or decreased according to the desired number of blow mold rows.
It is a further object of the invention to vary the number of center row distances in the conditioning, stretch blow, and bottom plug units according to the number of center rows of the preform molds.
It is yet a further object of the invention to turn the conditioning and stretch blow mold units to match the number of perform mold rows.
It is yet a further object of the invention to reduce the number of blow mold cavities to a fraction of the number of perform mold cavities.
It is a further object of the invention to collect at least two rows of molten preforms in the openings of the tray plates of the tray unit at the center row distance of the preform mold cavities and telescope the molten preforms into the center row distances of the blow mold cavities during the retracting movement of the tray unit out of the molding area. It is a further object of the invention to add additional blow mold units for multi-stage stretch blow mold applications.
It is a further object of the invention to add a secondary robot with a secondary universal gripper assembly to transfer pretreated hollow articles from the first blow mold unit into subsequent blow mold and discharge units.
It is a further object of the invention to add component transfer devices to pick up components during the blow-molding phase and to introduce these components into the open blow molds during the waiting phase.
It is a further object of the invention to insert components on the neck inside of preforms before the shrinkage phase of the molten material has been completed.
It is a further object of the invention to insert components on the inside of the preform walls prior to the conditioning and stretch blow-molding phase.
It is a further object of the invention to pivot the gripper assembly to pick-up reheated preforms from a lateral reheat oven assembly.
It is a further object of the invention to mount the upper conditioning and blow-clamp assemblies onto linear bearings, so enabling the movement of said clamp assemblies laterally to facilitate mold and machine component mounting.
2. Brief Description of the Invention
In accordance with the present invention, molten material is introduced into single-row or multi-row preform mold cavities. Upon completion of the solidification phase, the upper mold half is raised together with the injection cores. Immediately thereafter, during the mold-opening stroke, a tray unit with at least one row of tray plates enters between the movable mold halves collects the molten preforms through corresponding openings in the tray plates and retracts immediately out of the molding area. The preforms are either held onto the tray plates by their transfer beads or in the absence of such transfer beads by their bottom gate sections in catch baskets mounted beneath the corresponding openings of the tray plates. A robot with a universal gripper assembly then lifts either all or consecutively a fraction of the preforms out of the retracted tray unit and transfers the preforms to the conditioning unit, while the preform mold is closed again to mold the next set of preforms. The robot with the universal gripper assembly holds the preforms in the conditioning unit just long enough for the internal touch rods and external heater pots to monitor the temperature profile in the preforms. Next, the robot with the universal gripper assembly brings the conditioned preforms into the blow molds, wherein, after the bottom plugs have been raised and the blow molds have been closed, the blow cores and stretch rods descend to enter the preforms at their open ends, low and high pressure blow air comes on and forms finished hollow articles. Immediately upon completion of the stretch blow cycle, the blow cores and stretch rods lift out of the blow molds, the blow molds are opened, and the robot with the universal gripper assembly lifts the finished hollow articles out of the blow mold cavities to transfer the same into the oriented discharge unit. The robot with the now empty universal gripper assembly returns to a waiting position at the preform molding and tray unit Due to the fast cooling nature of certain materials, such as PET or PEN, among others, the time periods necessary for conditioning, stretch blowing, cooling, and oriented discharging, as well as for the short and quick transfer strokes of the servo controlled robot with its light-weight universal gripper assembly and with its reduced inertia happen within a fraction it takes to mold the preforms. This benefit allows picking up the molten preforms with the universal gripper assembly in fractions as well and transferring the same through the downstream processing units having a lesser number of blow mold cavities than preform cavities.
In addition to the preform supply from the molding unit, outsourced preforms from an adjacent reheat unit can be supplemented. During this intermediate phase, the universal gripper assembly pivots and picks up reheated preforms from said reheat unit and transfers them the same way in a short linear movement through the conditioning, stretch blow, and oriented discharge phases.
In view of the freely programmable and time-independent movement of the robot with the universal gripper assembly, following component transfer devices can be added. During the stretch blow phase, these transfer devices pick up components such as labels, handles, valves, etc. When the robot with the universal gripper assembly has returned to the waiting position, the components are released into each blow mold half, all without any increase in the total cycle time.
The above described process shows that the number of blow mold cavities is either equal to or a fraction of the number of preform mold cavities. To further boost production and to gain maximum utilization of the preform-molding unit, stack-blow molds are installed to meet the production of a larger number of preform mold cavities. The blow-mold clamp requirements are virtually the same with single-row or multi-row blow mold assemblies. A selectable number of helical spindles with helical nuts and pivoting spacer platens, located between the blow mold rows, provide instant mold opening and closing as well as parting-line alignment with the entering bottom plugs, blow core and stretch-rod assemblies mounted in a stationary position. A synchronized movement of the enveloping tiebar mounted blow-mold clamp platens and generated by the closing means provides the final blow-mold clamping pressure. The helical spindles with helical nuts mounted onto the blow mold clamp platens accelerate the blow mold opening and closing strokes in conjunction with the pivoting spacing platens movements. The spacing platens being connected to the intermediary blow mold clamp platens follow and are reversed by the diverging and converging clamp movement at low friction. A central step motor and gear pulleys mounted beneath onto each spacing platen enveloped with a common drive belt amplifies the pivoting movement against mechanical stops (not shown) to ascertain perpendicularity positioning during the mold closing phase. The fully mechanical stack blow mold assembly with its synchronized clamp movements and mold height adjustments via tooth belted tie bar nuts and electrical drive is also well suited for heat set container production. The stretch blow assemblies located above the stack blow mold clamps are adjustable within the center row distances to align with the respective blow mold parting lines.
The injection cores, conditioning and stretch blow rods are held onto individual clamp bars. The clamp bars are bolted individually onto the machine clamp platens according to the center distance rows of the blow-mold cavities. The neck splits or stripper plates and the blow cores are also mounted on individual clamp bars. These clamp bars are bolted individually onto frame-type machine clamp platens within the respective units. This flexibility in varying the center row distances in the individual processing units or by telescoping the tray plates of the tray unit into the center row distances of the down stream units during the molten preform discharge stroke as well as telescoping the universal gripper means from the center distances of the preform molds to the center distances of the blow molds permits the mounting of existing molds from other stretch blow processes, or adding or deleting mold cavity rows, thereby increasing or decreasing mold opening daylights for the production of larger and smaller hollow articles, respectively.
The injection, conditioning, stretch blow and oriented discharge units can be turned based on the preform mold design to minimize the number of universal gripper assemblies.
Certain molten materials such as PC or PP, heavy-wall returnable PET bottles or heat-set PET bottles may require stepped processing treatments to achieve specifications. In this case, additional blow-mold units and a secondary robot with a universal gripper assembly are installed. In this processing mode, once the primary robot with the universal gripper assembly has transferred the preforms into the first blow-mold assembly, it returns to the waiting position at the preform-molding machine. A secondary robot with a universal gripper assembly picks up the pretreated preforms and transfers them directly to one or several subsequent blow mold units and finally to an oriented discharge unit.
Hollow articles tend to deform in non-stretch blow-molded areas such as the neck finishes during hot-fill operation. A unit capable of transferring internal components into preforms may be installed right after the preform-molding unit and above the tray unit. An internal component transfer device picks up heat-stable sleeves from a sorting conveyor and incorporates the same into the open-ended preforms at elevated neck temperatures, thus before the shrinkage phase has been completed. The robot with the universal gripper assembly picks up the sleeve-reinforced preforms and transfers them to a conditioning unit, wherein the cooling neck finishes shrink tightly onto the heat-stable sleeves. After passing through one or several stretch blow units, neck heat-stable hollow articles are released into an oriented discharge unit.
To enhance the barrier properties of hollow articles, a thin inner liner of high-barrier material can be inserted the same way into the preforms by the internal component transfer device prior to transferring the same into a conditioning and stretch blow unit.
The above-described stretch blow molding method and apparatus provides the molder with maximum production flexibility by forming hollow articles in either single-row or multi-row blow-mold assemblies as well as processing versatility in adding additional stretch blow mold units and introducing external and internal components to the hollow articles. The open architecture of the individual processing units permits the installation of molds from different machine designs and requires one set of neck splits in the preform mold only. The completely separate preform molding unit from all other processing units and preform pick-up from a tray unit allows quick mold opening and closing of the preform mold clamp. All the downstream phases described above happen within the preform-mold filling, forming, cooling and take out phases. Thus, the preform-molding phase and the rapid mold opening preform take-out by a tray unit and mold-closing phase constitutes the total processing cycle.
Adding an additional reheat unit further increases the output capabilities of the stretch blow-molding machine to meet seasonal market demands.
Prior art for robotic gripper assemblies requires removal of preforms from a molding unit or finished hollow articles from an ejection or blow-mold station of a stretch blow-molding machine when in a static position and placing them onto conveying means. The improvement described herein involves the use of a tray unit and a robot with a universal gripper assembly to pick up molded preforms in total or in fractions in an upright position from a tray unit which have been collected from a preform molding unit during the mold-opening stroke or from a reheat oven and transferring them at freely programmable intervals to a multitude of individual processing units performing multiple functions, such as conditioning, stretch blowing, adding internal or external components, or hand-over pre-treated hollow articles to subsequent stretch blow units prior to final release of the finished hollow articles. In this capacity, the tray unit and the robot with the universal gripper assembly replaces the use of heavy rotary transfer plates carrying neck splits for each station, or circulatory carriers with neck-mold moving pieces, or carriages with neck-size-dependent support jaws, each being linked together in a closed circuit.
Prior art for multi-row blow-mold clamps requires that each blow mold row be first closed by pneumatic external moving means. Subsequently, a pancake cylinder assembly is raised in between the rows which are expanded to apply the necessary clamp pressure against opposite clamping cylinders on each end, or a power transmission means is used to actuate, through motion-transferring means, a double pair of mold halves only.
In accordance with the present invention, a multitude of helical spindles with helical nuts and pivoting spacing platens are mounted to instantly create a mechanical blow mold row opening and closing action within selected center distance rows. Synchronized peripheral clamping means are used simultaneously to apply the necessary opening and closing force. A further refinement involves the flexibility of adding or deleting spacing platens depending on the desired number of blow-mold rows. The benefits to the molder are to adapt production outputs to market demands within the same stack-mold clamping means. The higher output rate capabilities of stack-blow-mold assemblies make in-line hollow article filling and pasteurization economical with the one-step and one and a half step process.